Warning THIS VIDEO AND ARTICLE MAY CONTAIN SPOILERS
Hero 300 is the "ending" chapter of the game Half-Minute Hero. You start as the Hero after being revived by the Sage and the Knight , you then have to find the other heroes: Evil Lord and Princess in order to finish off the Ultimate Evil Lord.
In this mode you only have 300 seconds to finish the Ultimate Evil Lord, and as seen in the Knight story line, the Time Goddess is unable to rewind time. Also every area of the level disappears every 60 seconds. There are also 4 optional superbosses to defeat depending on your overall rank in the previous modes. These bosses are harder than the final boss and add 30 seconds to the time when defeated.
Thanks to StarofViolence for the speed run video